1. Field of the Invention
As the distribution of available fossil fuels changes, different approaches to the generation of electricity become of increasing interest. One of the potential sources for electricity is fuel cells. While fuel cells employing solid-oxide electrolytes have many attractive features, a major drawback is the high operating temperature required. At the high temperatures, constituent materials have limited lifetimes. The materials tend to diffuse into each other destroying their integrity and function.
Furthermore, in developing fuel cells, it is desirable to have complete utilization of the fuel, so that the effluent is free of any fuel value. Also, one wishes to have the greatest proportion of the theoretical energy resulting from the oxidation of the fuel to a final product converted to electrical energy, rather than dissipating energy as unrecoverable heat. However in some instances, the fuel cell may be employed for producing an intermediate product as well as electricity.
It is therefore desirable to develop new fuel cells having improved properties in operating condition, efficiency of fuel utilization, and efficiency of transformation of the energy resulting from the reaction into electrical energy, as well as providing reduced costs.
2. Description of the Prior Art
Nernst, Z. Electrochem. (1900) 6:41 reported the electrolytic evolution of oxygen from a solid zirconia-yttria composition. A summary of the solid-state chemistry of stabilized zirconia is provided by Kofstad, Nonstoichiometry, Diffusion and Electrical Conductivity in Binary Metal Oxide, Wiley-Interscience (1972), pp. 160-165.
The electrical properties of solid oxide electrolytes is presented by Etsell and Flengas, "The Electrical Properties of Solid Oxide Electrolytes," Chem. Rev. (1970) 70:339-376. The conductivities of several stabilized-zirconia electrolytes as a function of temperature may be found in Nasrallah and Douglas, J. Electrochem. Soc. (1975) 121:255-262, while the conductivity relationship for other oxide systems may be found in U.S. Pat. No. 3,607,424 and Ross and Benjamin, "Thermal Efficiency of Solid Electrolyte Fuel Cells With Mixed Conduction" (United Technologies Research Center, East Hartford, Conn. 06108).
Electrochemical studies on solid electrolytes were the subject of the following seminars: National Fuel Cell Seminar, July 11-13, 1978, Hotel Regency, San Francisco, Calif.; National Fuel Cell Seminar, July 14-16, 1980, San Diego, Calif.; "Third International Meeting on Solid Electrolytes-Solid State Ionics and Galvanic Cells," Sept. 15-19, 1980, Tokyo, Japan.
Weissbart and Ruka, J. Electrochem. Soc. (1962) 109:723 investigated current-over potential behavior in hydrocarbon systems. Pancharatnam, et al. J. Electrochem. Soc. (1975) 122:869-875 describe the electrolytic dissociation of nitrogen oxide on scandia-stabilized electrolytes. Wen and Mason, J. Appl. Electrochem. (1978) 8:81-85 describe the role of scandia-stabilized zirconia electrolyte in electrocatalytic processes. Goffe and Mason, J. Appl. Electrochem. (1981) 11:447-452 describe the use of scandia-stabilized zirconia for the electro-oxidation of hydrocarbon fuels derived from coal, operating at 700.degree. C. and one atm. Ong, et al., Solid State Ionics (1981) 3/4:447-452 describe the electrocatalytic role of stabilized zirconia on the anodic current-overpotential behavior in hydrocarbon fuel cells.